A typical side-gusset bag made of film comprises two face panels and first and second side gussets between longitudinal edges of the face panels and is attached to the face panels by longitudinal welds. The first side gusset has a handle loop created by cuts in the outer film and a patch of an inner film covers the hole in the first side gusset created by the handle loop.
A film bag comprising the above-described features has been disclosed in EP 1,777,167 and U.S. Pat. No. 5,048,976. A relatively simple manufacture process is possible due to the fact that the handle loop is created by simple cuts in a side gusset. On the other hand, the opening created by the cuts must be sealed on the inside, and for this purpose the prior art provides strips or patches of film on the inside of the film bag. Providing separate film strips is difficult depending on the type of manufacture process. Another disadvantageous aspect is that providing film strips results in stepped levels and transitions being created on the side gusset such that the film strips for creating the seal must also be provided with a circumferential seal. These stepped levels and welds can be disadvantageoous specifically in terms of handling the bag.
There are a variety of manufacture methods for producing side-gusset bags. The entire film bag can, for example, be formed from a single film web by folding. The present invention, however, relates preferably to an embodiment of the bag in which the face panels and the side gussets are made of separate film sections.
U.S. Pat. No. 7,775,957 describes a method for producing film bags in which a bag web is created such that successive bags are adjacent to each other with their longitudinal edges touching. The direction of manufacture here corresponds to a transverse direction of the individual bags. The web is created first that comprises successive, initially attached bag blanks. A first film web is moved in the manufacture direction. A strip is then fed such that the edges of the strip are folded over onto a central section of the strip. The edges are typically of the same width such that a gap still remains between the edges after folding.
Following this, sections of the strip are applied to the first film with equal spacing perpendicular to the manufacture direction (that is longitudinally of the bag) before a second film is fed in the manufacture direction to cover the first film web and the sections of the strips. Longitudinal welds are then made perpendicular to the manufacture direction by which the sections of the strips are welded both to the second film web at the folded-over edges and also to the first film web on its opposite side. From the web thus created, individual film bags are then separated by a transverse cut in the region of the strips so as to create two side gussets of successive film bags from one folded strip.